Adds Media.Audio.InputStartWasDeferredAudioWorkedMac UMA stat

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index b03657f4587f0a44562baea79a418a2bf7e39e90..e7fae0652345bce83ac024721b2f64982baf0a6c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -19034,6 +19034,19 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.Audio.InputBufferSizeWasChangedAudioWorkedMac"
+    enum="BooleanChanged">
+  <owner>henrika@chromium.org</owner>
+  <summary>
+    Indicates if the size of the audio unit's IO buffer was changed when
+    starting an input audio stream. Sampled each time an AUAudioInputStream
+    instance is closed, i.e., we know that input audio has started as it should
+    when this value is stored. Can be compared with
+    Media.Audio.InputBufferSizeWasChangedMac which is only added when input

[Ilya Sherman, 2016/03/02 22:57:24]

These metric names are now rather confusing, since the general-sounding metric
is only logged on failure.  It might be nice to rename the existing metrics for
clarity.  (OTOH, renaming the metrics results in a discontinuity in terms of the
data, which might be inconvenient enough to not be worth the trouble.)

[henrika (OOO until Aug 14), 2016/03/03 09:44:39]

I realize that and I would have selected other names if I could start from
scratch. I tried to provide very detailed comments to make it less confusing.
Would like to stick with the existing names to avoid hiccups in the data. Hope
that is OK. 

+    audio fails to start.
+  </summary>
+</histogram>
+
 <histogram name="Media.Audio.InputBufferSizeWasChangedMac"
     enum="BooleanSuccess">
   <owner>henrika@chromium.org</owner>
@@ -19073,6 +19086,18 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.Audio.InputStartWasDeferredAudioWorkedMac"
+    enum="BooleanDeferred">
+  <owner>henrika@chromium.org</owner>
+  <summary>
+    Indicates if audio capturing started with a small delay or not. Sampled each
+    time an AUAudioInputStream instance is closed, i.e., we know that input
+    audio has started as it should when this value is stored. Can be compared
+    with Media.Audio.InputStartWasDeferredMac which is only added when input
+    audio fails to start.
+  </summary>
+</histogram>
+
 <histogram name="Media.Audio.InputStartWasDeferredMac" enum="BooleanSuccess">

[Ilya Sherman, 2016/03/02 22:57:24]

Please use BooleanDeferred here too.

[henrika (OOO until Aug 14), 2016/03/03 09:44:39]

Will do but I was not sure how that would affect existing results. I guess that
is safe, right?

   <owner>henrika@chromium.org</owner>
   <summary>
@@ -59781,6 +59806,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="1" label="Data Reduction Proxy"/>
 </enum>
 
+<enum name="BooleanDeferred" type="int">
+  <int value="0" label="Not deferred"/>
+  <int value="1" label="Deferred"/>
+</enum>
+
 <enum name="BooleanDelete" type="int">
   <int value="0" label="Ignored"/>
   <int value="1" label="Deleted"/>